Contraceptive vaccines

The basic principle of a contraceptive (or anti-fertility) vaccine is to use the body's own immune defence mechanisms to provide protection against an unplanned pregnancy. Factors such as: economic production, convenience of use, relatively long-lasting but reversible action, low failure rate, and the avoidance of mechanical devices or exogenous hormones make this approach a potentially attractive option for family planning programmes in both developing and developed countries. The major efforts in research and development have involved the prospect of active immunization against specific antigens of sperm, ovum, zygote and early embryo, and the pregnancy hormone hCG. Several anti-hCG vaccines have entered clinical trials and show promising results. These vaccines operate by preventing or interrupting pregnancy at the peri-implantation stage probably by neutralizing the luteotrophic action of hCG. The most refined vaccine is one directed against the unique C-terminal peptide on the beta-subunit of hCG. This vaccine provokes antibodies that are specific for hCG and do not cross react with hLH. Future research efforts aim to optimize the anti hCG approach, utilize new vaccine delivery systems, and broaden the spectrum of target antigens of potential utility for contraceptive vaccines.

Vaccination for birth control

The global population is currently expanding at the unprecedented rate of nearly 1 billion per decade, with 94% of the increase occurring in the developing world. New methods of fertility regulation are urgently needed, and the development of birth control vaccines by active immunization against antigens specific for reproduction has made substantial progress during the last two decades. These vaccines are meant to have an outstanding impact on future control of worldwide population growth by providing safe, effective, long-lasting and reversible contraception. The most advanced of these vaccines are based on the placental pregnancy hormone human chorionic gonadotropin (hCG), and have already entered clinical trials. However, immunological cross-reactivity and lack of efficacy of anti-hCG antibodies seriously challenge this strategy. Conversely, efforts to understand the molecular events involved in the fusion of sperm and egg have led to the identification of new target structures for the development of fertility-regulating vaccines. Herein, we summarize the current state of birth control vaccines and discuss the risks and drawbacks of this approach to fertility regulation.

Reproductive rights and population control in Zimbabwe

The author argues that population control in Zimbabwe, in other developing countries, and even in developed countries is targeted at non-whites and at the poorer classes. She discusses fertility vaccines and male sterilization in this context, and makes the point that while the technology of population control flows from the North to the South, resources from the South are flowing North to maintain the economic status quo. "I think that the real population problem is the widening gap between a few greedy, irresponsible people, most of whom happen to be located in the North, and the rest of humankind, whose lives have been so denigrated that they are now merely statistics.... We can easily see that what should be feeding, clothing, housing, healing, pleasing Africans, goes North, all in the name of ¿development'."

The suitability of human chorionic gonadotropin (hCG)-based birth-control vaccines

It has been widely hoped that immunological methods of fertility regulation by active immunization against specific antigens of the oocyte, sperm, zygote and early embryo, and the placental pregnancy hormone human chorionic gonadotropin (hCG), will provide a means to control the problem of worldwide population growth. The most advanced candidate vaccines are based on hCG immunogens and have entered clinical trials. However, during the past few years, increasing evidence has emerged that the current approaches using hCG as the target molecule may have some major drawbacks. On the basis of their recent findings, Stephan Dirnhofer and colleagues raise doubts on the suitability, safety and efficacy of gonadotropin-based immunological contraceptive vaccines.

Vaccination for contraception

Vaccination for birth control has several advantages over currently available methods of family planning and should prove an attractive addition to the contraceptive armamentarium both in developing countries and in a developed country such as Australia. Concerns have been voiced by consumer health advocates that vaccines, like other long acting contraceptive methods, may be abused by health authorities in developing countries and by their use in vulnerable groups such as aborigines in our own country. These concerns need to be recognised and addressed. More difficult to accommodate are the anxieties expressed by feminist groups about the 'loss of control' and 'lack of body awareness' inherent in a method, such as a vaccine, that is relatively easily administered and has no overt side effects. There is no evidence that these concerns are shared by women in general. The antifertility vaccine that will most likely be applied first in family planning programmes is one directed against the pregnancy hormone hCG. A WHO vaccine directed against the C-terminal peptide of beta-hCG provokes a specific and safe immune response and will enter Phase 2 trials in Sweden this year. Subsequent developments with this vaccine will include the replacement of the current emulsion vehicle by a delivery system based on biodegradeable microspheres which will give a more sustained antigen release and duration of effectiveness.

Implantation, interception and contraception

The factors involved in post-fertilization events leading to implantation in mammals are discussed with special reference to potential forms of interception. The stages of embryonic growth until implantation are considered initially. The growth and differentiation of the uterine endometrium is then described, followed by the events occurring during the apposition and invasion of the implanting embryo. Several potential approaches to new forms of interception are considered, and the advantages and disadvantages of each of them are evaluated. Among them, new vaccines against the zona pellucida, inactivation of the secretions of the blastocyst, hatching, the activity of pinopodes, and the endometrial proteins produced in the secretory phase seem to offer various and varied targets. Some existing methods of fertility regulation may act by affecting these stages of development, e.g. RU486 may interfere with pinopod function. Various physiological and embryonic consequences of interfering with these stages of pregnancy are discussed.

Antibody response against three epitopic domains on human chorionic gonadotropin (hCG) in women and rodents immunized with a beta hCG-based immunocontraceptive vaccine

The antibody repertoire generated against human chorionic gonadotropin (hCG), following immunization with an immunocontraceptive vaccine based on the beta subunit of the hormone, in humans was compared with that generated in rats. Three epitopic domains represented by the beta hCG loop peptide 38-57, the carboxy-terminal peptide (CTP) 109-145, and a region defined by monoclonal antibody (MAb) 206 were probed. In both species, the titer of antibodies against the MAb 206-defined epitopic domain had a good correlation with the total anti-hCG antibody titers. However, the antibody response against the beta hCG loop peptide (38-57) was not observed in human subjects and there was a weak response against this peptide in rats. Despite the good anti-hCG antibody titers in all animals (n = 8), only two had antibodies against this domain. A good antibody response was observed against CTP in rats, whereas in humans this region was weakly immunogenic. Antibodies against CTP were detected in random samples in only 57% of the subjects and this response had no correlation with the total anti-hCG antibody titers. The high antibody response against CTP in rodents compared to humans may be due to its recognition as a foreign determinant. Our results demonstrate that contraception can be achieved in women despite a poor antibody response against the CTP (109-145) and a receptor binding domain (38-57) of beta hCG.

The value and use of different contraceptive methods

Reductions in the rates of maternal and child mortality as well as in demographic growth are directly linked to contraceptive usage. The development and availability of safer, improved contraceptives which are convenient to use could be expected to be used by a larger group of individuals and thus make an impact on reproductive health as well as on population growth rates. Such arguments have been used to support contraceptive research. This article deals with some of the developments that have occurred as a consequence of such efforts.

Tissue specificity of the acrosomal protein SP-10: a contraceptive vaccine candidate molecule

The tissue specificity of the intra-acrosomal protein SP-10 was examined by Northern blot and polymerase chain reaction (PCR) analysis. Messenger RNA from 36 tissues in the female baboon (Papio papio) was isolated, separated on agarose gels, transferred to nylon, and probed with either SP-10, beta-actin, or cyclophilin cDNA. Northern blots, which were processed at both low and high stringency, showed SP-10 to be expressed exclusively in the testis. The mRNA from each tissue was also reverse transcribed, and both SP-10 and beta-actin were amplified by PCR from the resulting cDNA. Ethidium bromide-stained agarose gels of the SP-10 PCR products showed three clear bands from the testis but no co-migrating bands from the other tissues. Southern blots of the PCR products showed that only the three bands in the testis were related to SP-10. The data demonstrate that the SP-10 gene products are testis specific, a characteristic essential for a contraceptive vaccine candidate molecule.

Immunization against HCG

The possibility of using the immune system to provide protection against an unwanted pregnancy has been postulated since the very early days of modern immunology. During the past two decades or more, a major goal-directed research effort, involving several independent groups of investigators, has been underway with the objective of developing birth control vaccines suitable for use by men and women at all stages of their reproductive lives. The most advanced work in this area is concerned with the development of a vaccine directed against human chorionic gonadotrophin (HCG), a hormone that is produced by the peri-implantation embryo and that is essential for successful implantation and the establishment of early pregnancy. These studies have reached the stage of clinical testing of a number of prototype vaccines based on different parts of the HCG molecule. No adverse side effects have been observed or reported in these clinical trials and larger scale clinical studies are being planned to assess further the safety, efficacy and acceptability of these preparations. Research is also underway to develop improved versions of these HCG vaccines that will offer 12-18 months protection following a single injection. The stage is set for the introduction, by the turn of this century, of the first totally new method of family planning in four decades.

Salmonella may offer contraceptive

A reversible, inexpensive birth control vaccine for men and women may come from an unlikely source--genetically altered salmonella bacteria. The bacteria cause food poisoning, typhoid and diarrhea. But with some genes removed and others spliced in, an altered form produces proteins that make the immune system reject sperm and does not cause disease, says Dr. Roy Curtiss, a biology professor at Washington University in St. Louis, Missouri, US. The approach was announced in November at a US meeting of the Council for the Advancement of Science Writing. "Salmonella act as the factory, making specific antigens. It is a slow-release system," he says. The altered bacteria produce sperm antigens, and both male and female immune systems make antibodies against them. To sustain immunity, a booster vaccine might be necessary every 6 to 12 months. Numerous concerns, however, have been raised over the use of such live vaccines. A live vaccine, for example, could accidentally immunize people through fecal contamination of water or food. Researchers are testing the vaccine approach in mice and are scheduled to begin experiments soon with macaque monkeys and baboons. Experiments among humans are not yet scheduled and would not begin until ethical and health issues are resolved. The contraceptive vaccine could be inexpensive to produce and would require no refrigeration, making it easy to store. It would probably be administered orally, eliminating costs and risks associated with injections, Dr. Curtiss says.

Contraceptive vaccine development

Recent advances in antigen definition and production have made the development of a contraceptive vaccine more attainable. Such a vaccine must evoke an immune response that blocks an indispensable step in the reproductive process. Vaccine research involves many approaches to fertility prevention. Vaccines are being developed that could interrupt fertility by inhibition of gonadotrophin release, the function of follicle-stimulating hormone or the effects of human chorionic gonadotrophin (hCG); alternatively, they may prevent fertilization by interfering with the transport of spermatozoa or with sperm-zona pellucida binding. The most advanced prototype is a vaccine based on antibodies to beta hCG. Such vaccines are being studied for clinical efficacy. Many hurdles remain in contraceptive vaccine development. Since the antigens are peptides or small proteins, the resultant immune response is usually moderate, and better adjuvants and delivery systems must be developed to enhance and maintain the immune response. Improvement of the mucosal immune response may be necessary for vaccines incorporating sperm antigens. Research on vaccines that control fertility has resulted in a fascinating base of scientific knowledge that, it is hoped, can be converted into products that will allow another option for individuals who wish to control their fertility.

A birth control vaccine is on the horizon for family planning

Vaccines for control of fertility are likely to have an important impact on family planning methods. They are designed to act by mobilization of an internal physiological process and do not require external medication on a continuous basis. A number of birth control vaccines are at different stages of development, the most advanced being a vaccine inducing antibodies against human chorionic gonadotrophin (hCG). This vaccine consists of a heterospecies dimer (HSD, beta hCG associated with alpha-subunit of ovine luteinizing hormone, beta hCG:alpha oLH) linked to tetanus toxoid (TT) or diphtheria toxoid (DT) as carriers. The vaccine has recently passed an important milestone; it has completed the first leg of phase II efficacy trials. Women of proven fertility leading active sexual life were protected from becoming pregnant at antibody titres > or = 50 ng of hCG bioneutralization capacity per ml. This vaccine has previously been demonstrated to be reversible in its effect. It is free from any notable side-effects on endocrine, cardiovascular and other body functions. Ovulation was not disturbed and menstrual regularity was maintained. A logistic disadvantage of the present vaccine is the requirement for multiple injections. This is expected to be overcome by encapsulation of the requisite doses of the vaccine in biodegradable microspheres, which could be given at a single contact point for sustained antibody titres lasting over a year. A live recombinant vaccine has also been made that elicits high anti-hCG titres in monkeys for nearly 2 years following primary immunization and a booster at 8-9 months.

Anti-sperm and anti-ovum vaccines: the selection of candidate antigens and the outcome of preclinical studies

A clear conceptual basis for anti-sperm and other modes of immunological birth control exists in spite of the limited basic research done on surface antigens of sperm or egg. In the normal physiological condition, the immune system does not respond to sperm, egg or fetus. Compared with anti-egg or anti-fetus immunocontraception, an anti-sperm vaccine has two theoretical advantages. First it would work in both males and females; second, it would not raise problems of autoimmunity in the female if a sperm-specific protein is used. However, for the development of such contraceptive vaccines the following scientific questions need to be resolved: (1) what surface protein to use as an antigen; (2) what adjuvant to use in humans for an anti-fertility vaccine; (3) how to maintain a high titre; (4) how the contraceptive effect will be terminated; and (5) what are the potential side-effects.

Anti-trophectoderm vaccines: rationale and methods used for antigen identification and selection

Trophoblast, forming a continuous interface at the maternal-fetal junction, is of considerable interest to biologists. An area of recent research is the search for trophoblast-specific antigens. It is believed that identification and characterization of these antigens may have many practical applications such as in development of contragestational vaccines. To be acceptable for humans such a vaccine will need to be effective before the completion of implantation and appearance of the primitive streak about 14 days after fertilization. This will not alter the menstrual cycle or the time of menses. Vaccines having a later effect resulting in termination of pregnancy after this time would be considered abortifacients. Although logistical and ethical considerations necessitated the use of post-implantation human trophoblast in WHO Birth Control Vaccine studies, the antigens isolated from such tissues would need to be expressed and be detectable on the surface of pre-implantation trophectoderm if they are to represent appropriate candidates for vaccine development. The criteria for identification and selection of these antigens will be reviewed.

Anti-LHRH and anti-pituitary gonadotropin vaccines: their development and clinical applications

Active immunization against hormones involved in the regulation of reproduction is a promising approach to immunocontraception. The hypothalamic peptide, LHRH, controls the synthesis and release of the pituitary gonadotropins, LH and FSH, which regulate gonadal steroidogenesis, sperm production, follicular development and ovulation. Immunizing female primates against LHRH or LH induces infertility, but also disrupts the menstrual cycle. Immunization against the beta subunit of the placental hormone, chorionic gonadotropin (hCG), or its fragment prevents pregnancy without interfering with menstrual cycles or ovulation. hCG vaccines have reached the stage of clinical trials. FSH and LHRH have been tested for immunocontraception in male primates. While active as well as passive immunization against FSH reduced spermatogenesis severely, azoospermia could not be achieved consistently. Immunization against LHRH effectively suppressed spermatogenesis in rats and rabbits. Normal sexual behaviour was maintained by concomitant androgen administration. Fertility was restored when antibody titres declined and no adverse effects were observed. A number of LHRH vaccine preparations are being tested in men in several countries, including the United States. Since the LHRH vaccine reduces serum testosterone levels the first clinical studies involve men with prostate cancer. These trials will be followed by immunization of normal men if the antibody response is sufficient and no adverse effects are observed.

Anti-hCG vaccines are in clinical trials

Two vaccines inducing antibodies against human chorionic gonadotropin (hCG) have completed Phase I clinical trials, indicating the reversibility and safety of these vaccines. One is currently in Phase II efficacy trials in women in three major centres in India. The available data suggest that the vaccine prevents pregnancy above antibody titres of 50 ng/ml hCG bioneutralization capacity.

Options for immunocontraception and issues to be addressed in the development of birth control vaccines

Although the number of family planning methods currently available to couples has never been greater, the range and type of options are still not adequate to meet the widely varying personal needs and demands of individuals worldwide. Birth control vaccines offer a number of theoretical attractions although the development, preclinical and clinical testing of such vaccines pose a number of unique problems requiring novel solutions. If the on-going studies in this area are successful, a valuable new family planning method may be available by the end of the current decade.

Vaccines against fertility

The first evidence for the efficacy of a birth control vaccine in humans is now available from the Phase II trials on the human chorionic gonadotrophin vaccine in India. Several sperm antigens have been identified as potential contraceptive immunogens and zona pellucida antigens have been reported that reversibly control fertility.

Vaccines for control of fertility and hormone dependent cancers

Two vaccines, namely one inducing antibodies against hCG and the other against GnRH, are now in clinical trials. The hCG vaccine has entered Phase II clinical trials in three centres in India after successfully completing Phase I clinical studies in several centres in India and in four countries abroad. The vaccine was found to be devoid of side-effects; its effect was reversible. The available data on 179 cycles indicate that the vaccine prevents pregnancy at antibody titres above 50 ng/ml. A genetically engineered version of the vaccine has also been approved for trials in human lung cancer patients of the type which make hCG. hCG is observed to be a growth factor for such tumours. The GnRH vaccine is usable in both males and females as the deca-peptide is common to both sexes. Following suitable experimental and toxicology studies, the vaccine is currently in Phase I/Phase II clinical trials in patients of prostate carcinoma. Where antibody GnRH antibodies were induced, the LH, FSH and testosterone levels declined. This was accompanied by a reduction in prostate specific antigen. Clinical improvement was observed in many cases. The vaccine has also entered Phase I clinical studies in postpartum women, with the objective to extend the lactational amenorrhoea and extend inter-child interval.

The WHO Task Force on Vaccines for Fertility Regulation. Its formation, objectives and research activities

Over the past 18 years, the WHO Task Force on Vaccines for Fertility Regulation has been supporting basic and clinical research on the development of birth control vaccines directed against the gametes or the preimplantation embryo. These studies have involved the use of advanced procedures in peptide chemistry, hybridoma technology and molecular genetics as well as the evaluation of a number of novel approaches in general vaccinology. As a result of this international, collaborative effort, a prototype anti-HCG vaccine is now undergoing clinical testing, raising the prospect that a totally new family planning method may be available before the end of the current decade.

Phase I clinical trial of a World Health Organisation birth control vaccine

A birth control vaccine incorporating a synthetic peptide antigen representing the aminoacid sequence 109-145 of the C-terminal region of the beta subunit of human chorionic gonadotropin (hCG-beta) was submitted to a phase 1 clinical trial. Thirty surgically sterilised female volunteers, divided into five equal groups for different vaccine doses, received two intramuscular injections six weeks apart. Over a six-month follow-up there were no important adverse reactions, and potentially contraceptive levels of antibodies to hCG developed in all subjects. In the highest vaccine dose group, the results gave promise of a contraceptive effect of six months' duration.